Tuning the spin crossover above room temperature: iron(II) complexes of substituted and deprotonated 2,6-bis(benzimidazol-2-yl)pyridine

Abstract

The complex [Fe(tzimpy) 2](ClO 4) 2 · 2H 2O (tzimpy = 2,4,6-tris-(benzimidazol-2-yl)pyridine) shows an abrupt spin crossover ( S = 0–2 transition) above room temperature centered at T c = 323 K with a hysteresis width of Δ T = 35 K. The neutral iron(II) complex with deprotonated bzimpy ligands (bzimpy = 2,6-bis(benzimidazol-2-yl)pyridine) exhibits a gradual spin transition on the first heating with T c = 424 K. There are irreversible changes between T = 503 and 523 K: the liberation of the crystal water, the color change (blue–green) followed by a structure change. Next thermal cycles are reproducible though, heating/cooling paths are different from the first heating.